Chemical Production of Graphene Catalysts for Electrochemical Energy Conversion

Recently developed FC technology is among many approaches aiming at solving the global energy challenges. FCs are electrochemical devices that convert chemical energy from fuel molecules into electrical energy via electrochemical reactions. FCs are, however, limited by the scarce and expensive platinum (Pt) electrocatalysts. Approach in this Ph.D. thesis is, therefore, in reducing Pt content to ultra-low loadings in the electrocatalysts and optimizing their electronic structures to efficiently utilize Pt. Syntheses of small Pt nanoparticles (NPs) were performed in order to increase the specific area of Pt. Syntheses of core-shell Au-Pt (Au@Pt) NPs, with atomically-thin Pt shells on Au NP cores were performed. The Au@Pt NPs were further chemically immobilized on a highly conductive graphene support to ensure efficient electronic structure of the catalyst. Graphene possesses unique properties, such as high charge carrier mobility, high conductivity, mechanical strength (130 GPa), and high surface area (2600 m2g-1 ).[1] Chemical inertness of graphene in polymer electrolyte membrane FC (PEMFC) operating conditions resulted in enhanced electrocatalyst stability. Chemical anchoring of Pt and Au@Pt NPs was achieved via L-cysteine linker molecules that provided pathways for fast electron transfers during the electrocatalytic reactions. Electrochemical properties of selfassembled L-cysteine monolayers immobilized on single-crystal Au(111) surfaces were studied in ionic liquids and their structures imaged by scanning tunneling microscopy (STM), to investigate the nature of L-cysteine bonds on Au. Synthesized electrocatalysts were characterized by spectroscopic, microscopic and electrochemical techniques. Electrocatalysis was examined by electrochemical oxidation of formic acid, methanol and ethanol, and oxygen reduction reaction experiments, for both anode and cathode catalyst applications respectively. Finally, the main goal was to investigate the electrocatalytic performance within the PEMFC systems. Direct formic acid, methanol and ethanol PEMFC station was established. As-synthesized grapheneimmobilized Au@Pt NPs exhibited high electrocatalytic performance and long stability in direct formic acid, methanol and ethanol PEMFCs.